導航抽屜空指針異常

Question

我的導航抽屜中有一個RecyclerView。我不斷收到空指針異常。我看過類似的問題，但似乎沒有解決方案，請幫助。我不知道問題是什麼。 Gradle具有所有必需的依賴關係。

activity_expert.xml

<android.support.v4.widget.DrawerLayout  xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:id="@+id/drawerlayout"> 

<!--Content Section--> 
<FrameLayout 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:id="@+id/mainContent"> 

    <include layout="@layout/toolbar"></include> 

    <!--Main Content--> 
    <android.support.v7.widget.RecyclerView 
     android:layout_height="wrap_content" 
     android:layout_width="match_parent" 
     android:id="@+id/mainContentView"> 
    </android.support.v7.widget.RecyclerView> 

    </FrameLayout> 

<!--Drawer section--> 

    <android.support.v7.widget.RecyclerView 
     android:layout_width="240dp" 
     android:layout_height="wrap_content" 
     android:id="@+id/drawer_recycler_view" 
     android:layout_gravity="start" 
     android:background="@color/white" 
     android:scrollbars="vertical"> 
    </android.support.v7.widget.RecyclerView> 

drawer_header.xml

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="200dp" 
    android:background="@drawable/slider_3_small"> 

</RelativeLayout> 

drawer_row.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="wrap_content" 
    android:paddingTop="8dp" 
    android:paddingBottom="8dp" 
    android:layout_height="wrap_content" 
    android:background="#ffffff" 
    android:orientation="horizontal"> 


<ImageView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/rowIcon" 
    android:paddingLeft="16dp" 
    android:src="@drawable/cow_icon"/> 

<TextView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:paddingLeft="12dp" 
    android:paddingTop="4dp" 
    android:textAppearance="?android:attr/textAppearanceMedium" 
    android:text="Medium Text" 
    android:id="@+id/rowText" 
    /> 

</LinearLayout> 

ExpertActivity.java

package com.lavineoluoch.myapplication.cowsoko; 

import android.app.ActionBar; 
import android.app.SearchManager; 
import android.app.SearchableInfo; 
import android.content.Context; 
import android.support.v4.widget.DrawerLayout; 
import android.support.v7.app.ActionBarActivity; 
import android.os.Bundle; 
import android.support.v7.app.ActionBarDrawerToggle; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.LinearLayoutManager; 
import android.support.v7.widget.RecyclerView; 
import android.support.v7.widget.SearchView; 
import android.support.v7.widget.Toolbar; 
import android.text.Layout; 
import android.view.Menu; 
import android.view.MenuItem; 

import com.lavineoluoch.myapplication.cowsoko.appUtils.DrawerAdapter; 


import java.util.ArrayList; 
import java.util.List; 


public class ExpertActivity extends AppCompatActivity { 
//Data used to populate RecyclerView 
String TITLES[] = {"Buy a Cow","Meet an Expert","Model Farms","Share","Rate","Settings"}; 
int ICONS[] = {R.drawable.cow_icon,R.drawable.expert_icon,R.drawable.farm_icon,R.drawable.share,R.drawable.rate,R.drawable.settings}; 


private Toolbar toolbar; 
private DrawerLayout drawerLayout; 
private RecyclerView recyclerView; 




@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_expert); 

    drawerLayout = (DrawerLayout)findViewById(R.id.drawerlayout); 
    recyclerView = (RecyclerView)findViewById(R.id.drawer_recycler_view); 

    ActionBarDrawerToggle drawerToggle = new ActionBarDrawerToggle(this,drawerLayout,R.string.app_name,R.string.app_name); 
    drawerLayout.setDrawerListener(drawerToggle); 
    drawerToggle.syncState(); 


    DrawerAdapter drawerAdapter = new DrawerAdapter(TITLES,ICONS); 
    recyclerView.setAdapter(drawerAdapter); 
    recyclerView.setHasFixedSize(true); 
    recyclerView.setLayoutManager(new LinearLayoutManager(this)); 

    toolbar = (Toolbar)findViewById(R.id.toolbar); 
    setSupportActionBar(toolbar); 
    getSupportActionBar().setTitle("Meet an Expert"); 
    } 


@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_expert, menu); 

    //Insert Search View into toolbar 
    MenuItem item = menu.findItem(R.id.action_search); 
    SearchView searchView = (SearchView) menu.findItem(R.id.action_search).getActionView(); 
    SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE); 
    SearchableInfo info = searchManager.getSearchableInfo(getComponentName()); 
    searchView.setSearchableInfo(info); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 

}

最後DrawerAdapter.java

package com.lavineoluoch.myapplication.cowsoko.appUtils; 

import android.provider.Telephony; 
import android.support.v7.widget.RecyclerView; 
import android.view.LayoutInflater; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.ImageView; 
import android.widget.TextView; 

import com.lavineoluoch.myapplication.cowsoko.R; 

import java.util.List; 

import butterknife.ButterKnife; 
import butterknife.InjectView; 

/** 
* Created by USER on 8/7/2015. 
* 
* This class is the RecyclerView Adapter 
*/ 
public class DrawerAdapter extends  RecyclerView.Adapter<DrawerAdapter.ViewHolder> { 

private static final int HEADER_TYPE = 0; 
private static final int ITEM_TYPE = 1; 
private String NavTitles[]; 
private int NavIcons[]; 


public DrawerAdapter(String NavTitles[],int NavIcons[]) { 
    this.NavTitles = NavTitles; 
    this.NavIcons = NavIcons; 
} 

//Called whenever a new instance of our ViewHolder class is created 
@Override 
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
    if (viewType == ITEM_TYPE){ 
     View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_row,parent,false); 
     ViewHolder viewHolderItem = new ViewHolder(v,viewType); 
     return viewHolderItem; 
    }else if (viewType == HEADER_TYPE){ 
     View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.drawer_header,parent,false); 
     ViewHolder viewHolderHeader = new ViewHolder(v,viewType); 
     return viewHolderHeader; 
    } 

    return null; 
} 

//Called when the SO binds the view with the data -- or, in other words, the data is shown in the UI 
@Override 
public void onBindViewHolder(ViewHolder holder, int position) { 
    if (holder.holderId == 1){ 
     holder.textView.setText(NavTitles[position - 1]); 
     holder.imageView.setImageResource(NavIcons[position - 1]); 
    } 

} 

@Override 
public int getItemCount() { 

    return NavTitles.length + 1; } 

@Override 
public int getItemViewType(int position) { 
    if (position == 0) 
     return HEADER_TYPE; 

    return ITEM_TYPE; 

} 


/** 
* A ViewHolder describes an item view and metadata about its place within the RecyclerView. 
* RecyclerView.Adapter implementations should subclass ViewHolder and add fields for 
* caching potentially expensive findViewById(int) results. 
* 
*/ 


public static class ViewHolder extends RecyclerView.ViewHolder{ 
    protected int holderId; 
    @InjectView(R.id.rowIcon)ImageView imageView; 
    @InjectView(R.id.rowText)TextView textView; 

    /** 
    * 
    * @param itemView 
    * @param viewType 
    */ 
    public ViewHolder(View itemView,int viewType) { 

     super(itemView); 

     this.holderId = viewType; 
     if (viewType == ITEM_TYPE){ 
      ButterKnife.inject(this,itemView); 
      holderId = 1; 
     }else { 
      holderId = 0; 
     } 
    } 
} 

}

我logcat的看起來像這樣

08-08 19：26：35.847 18694-18694/com.lavineoluoch.myapplication.cowsoko E/AndroidRuntime：致命例外：main java.lang.NullPointer異常 at android.support.v7.widget.RecyclerView.onMeasure（RecyclerView.java:1764） at android.view.View.measure（View.java:16030） at android.view.ViewGroup.measureChildWithMargins（ViewGroup.java ：5012） at android.widget.FrameLayout.onMeasure（FrameLayout.java:310） at android.view.View.measure（View.java:16030） at android.support.v4.widget.DrawerLayout.onMeasure（DrawerLayout的.java：868） 在android.view.View.measure（View.java:16030）

Answer 1

我使用此代碼來解決這個問題：

LayoutInflater layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE); 
View view = layoutInflater.inflate(R.layout.nav_header, mNavigationView);